One of my bugbears with the Castle USB stack is that at the lowest level USB is packet based, while DeviceFS is stream based, so it can make it very hard to work with devices which rely on the packet-based behaviour (i.e. where the length of a packet is significant)

There are discussions about if a 26bit sequencer working under Aemulor could use the 32bit Midi module. It should. But perhaps that the problem will be MidiSupport (still 26bit) and not the sequencer. All of this needs to be tested.